This invention relates to processes for cleaning glass-coating reactors, and more particularly to a process for cleaning such reactors with a reactive gas.
Two commonly used methods to apply coatings to flat glass substrates are Atmospheric Pressure Chemical Vapor Deposition (APCVD) and vacuum sputtering. In APCVD, gaseous or vapor coating reagents are carried to the heated glass surface by a flow of gas. The reagents react on the surface of the hot glass to form a thin coating. For example, silane (SiH4) and carbon dioxide (CO2) are delivered to a heated glass surface to make a thin silicon dioxide (SiO2) coating. An APCVD reactor can be integrated directly into the float-glass tin bath process for the manufacture of the coated flat glass substrate. One drawback is that the SiO2 product not only grows on the hot glass substrate surface, but also on the hot walls of the reactor. It also nucleates in the gas phase and deposits loose particles in the exhaust system. Eventually, debris from the deposits on the wall and in the exhaust system will shed particles on the manufactured glass making it an unacceptable product. This unwanted deposited material on the reactor walls and in the exhaust system must be removed periodically in order to make an acceptable quality coated glass product.
In vacuum sputtering, preformed flat glass sheets are passed into an evacuated chamber. A plasma (glow discharge) is formed from a plasma-producing gas such as argon, helium, etc., introduced into the evacuated system. The ions in the plasma are accelerated at a cathode “target” made from the substance that is to be deposited on the glass surface. The impact of the plasma ion dislodges material from the target. The dislodged material deposits on the glass surface, forming a thin coating. In reactive sputtering, a reactive gas chemically combines with the dislodged material from the target to form a new chemical species that deposits on the glass surface. For example, using a silicon (Si) target in a reactive nitrogen or oxygen atmosphere, silicon nitride (Si3N4) or silicon oxide (SiO2) is deposited on the glass surface. As with APCVD, the formed Si3N4 or SiO2 also deposits on the walls of the reactor as well as the sides of the Si target. This coating on the walls and target eventually interferes with the sputtering process and must be removed.
Current practice by the glass coating industry is to clean either the APCVD or sputtering reactor by taking the reactor offline and mechanically removing (scraping or abrading) the wall coating. This results in costly reactor down time.
In the APCVD case, the reactor walls are sprayed with nitrogen and scraped with special tools that withstand the high reactor temperature. Since the glass production line cannot be stopped during the cleaning operation, the scraped debris falls onto the surface of the glass and produces unwanted defects on the surface. This unacceptable product must be re-melted or thrown away. After a moderate number of cycles, manual cleaning is no longer effective and the reactor must be taken completely out of the process, cooled and rebuilt.
In the sputter case, the reactor must be taken completely offline, pressurized to ambient, opened up and mechanically cleaned. Although the actual mechanical cleaning does not take a large amount of time or labor, reassembling and evacuating the sputter reactor takes several hours. The literature does not teach any other method for cleaning these glass-coating reactors.
A known method for removing unwanted deposits in a chemical vapor deposition (CVD) reactor used for semiconductor manufacturing is to introduce a reactive gas into the reactor to etch away the unwanted deposits.
An example of CVD chamber etching using a plasma etch process follows SiO2 deposition on a semiconductor substrate in a plasma enhanced CVD (PECVD) reactor. See, e.g., Johnson et al., “Reducing PFC Gas Emissions From CVD Chamber Cleaning,” Solid State Technology, p.103 (December 1999). After the thin film deposition, the wafer is removed and the debris in the chamber is etched using a C2F6/O2-based or NF3-based plasma process or a remote NF3-based process. The fluorine source for in situ plasma etching is typically C2F6. However, NF3-based plasma etching processes have also been developed. See U.S. Pat. No. 5,413,670 to Langan et al. NF3 plasmas may be generated in situ or using a remote plasma source. See, e.g., Raoux et al., “Remote Microwave Plasma Source for Cleaning Chemical Vapor Deposition Chambers: Technology for Reducing Global Warming Gas Emissions,” J. Vac. Sci. Technol., 17(2), p.477, March/April 1999.
An example of CVD reactor debris removal using a thermal etch process follows SiNx deposition on a semiconductor substrate in a low pressure CVD (LPCVD) furnace. See, e.g., U.S. Pat. No. 5,868,852 to Johnson et al. and U.S. Pat. No. 5,861,065 to Johnson. LPCVD furnaces are batch reactors where about 100 wafers are processed simultaneously. After the deposition, the wafers are removed, and because the LPCVD furnaces operate at 500-800° C., the debris on the walls can be etched by introducing NF3 gas into the reactor at temperature (i.e., no plasma is required). Thermal etching can only be accomplished using fluorine compounds that decompose at the operating temperature of the furnace.
Accordingly, it is desired to provide a process for cleaning a glass-coating reactor using a reactive gas.
It is further desired to clean such a reactor without employing scraping tools.
It is still further desired to clean such a reactor without taking it offline or significantly reducing the temperature in the reactor.
All references cited herein are incorporated herein by reference in their entireties.